.flex{
  display: flex;
}

/* 主轴的方向（即项目的排列方向） */
.flex-row {
  display: flex;
  flex-direction: row;
}

.flex-row-reverse {
  display: flex;
  flex-direction: row-reverse;
}

.flex-column {
  display: flex;
  flex-direction: column;
}

.flex-column-reverse {
  display: flex;
  flex-direction: column-reverse;
}

/* 如果一条轴线排不下，如何换行 */
.flex-nowrap {
  flex-wrap: nowrap;
  /* 默认值，不换行 */
}

.flex-wrap {
  flex-wrap: wrap;
}

.flex-wrap-reverse {
  flex-wrap: wrap-reverse;
}

/* justify-content属性定义了项目在主轴上的对齐方式。 */
.justify-start {
  justify-content: flex-start;
}

.justify-end {
  justify-content: flex-end;
}

.justify-center {
  justify-content: center;
}

.justify-between {
  justify-content: space-between;
}

.justify-around {
  justify-content: space-around;
}

/* align-items属性定义项目在交叉轴上如何对齐 */
.align-items-start {
  align-items: flex-start;
}

.align-items-end {
  align-items: flex-end;
}

.align-items-center {
  align-items: center;
}

.align-items-baseline {
  align-items: baseline;
}

.align-items-stretch {
  align-items: stretch;
}

/* align-content属性定义了多根轴线的对齐方式。如果项目只有一根轴线，该属性不起作用 */
.align-content-start {
  align-content: flex-start;
}

.align-content-end {
  align-content: flex-end;
}

.align-content-center {
  align-content: center;
}

.align-content-baseline {
  align-content: baseline;
}

.align-content-stretch {
  align-content: stretch;
}


/* ///////////////////////// */

.flex-row-start {
  display: flex;
  flex-direction: row;
  align-items: flex-start;
  justify-content: flex-start;
}

.flex-row-center {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: flex-start;
}
.flex-column-center {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
}

.flex-row-center-center {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
}
.flex-row-center-end {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: flex-end;
}

.flex-row-center-between {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: space-between;
}
.flex-column-center-between {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
}
.flex-column-center-center {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

/* ////////////////////////////////////////////// */

.flex-row-stretch {
  display: flex;
  flex-direction: row;
  align-items: stretch;
  justify-content: flex-start;
}
.flex-column-stretch {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  justify-content: flex-start;
}

.flex-row-stretch-end {
  display: flex;
  flex-direction: row;
  align-items: stretch;
  justify-content: flex-end;
}

.flex-row-stretch-between {
  display: flex;
  flex-direction: row;
  align-items: stretch;
  justify-content: space-between;
}
.flex-column-stretch-between {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  justify-content: space-between;
}
.flex-column-stretch-center {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  justify-content: center;
}


/* ///////////////////////// */


/* 项目的属性 */
.flex-grow {
  flex-grow: 1;
}
